Cook mushrooms in.a small amount of water until tender slice, and saute for 3 minutes in melted butter or margarine.
Beat eggs slightly, add 1/2 the mushrooms and 1/4 cup milk or mushroom stock.
Combine remaining mushrooms with flour, add milk gradually over low heat, stirring constantly until sauce-thickens add salt and pepper.
Cook egg mixture in well-greased frying pan over low heat.
Finish omelet by allowing liquid to run underneath as edges, thicken, or by baking in moderate oven for a few minutes.
Place several tbsp. mushroom sauce in center of omelet, fold over and serve covered with mushroom sauce.